1. Field of the Invention
The present invention relates to a switching regulator controlling circuit which is capable of switching readily a boosting operation and a step-down operation of a boosting and step-down switching regulator over to each other in accordance with the relationship among an input voltage, an output voltage and an output current, and a switching regulator for use in the same.
2. Description of the Related Art
As to an example of a conventional boosting and step-down switching regulator circuit, there is known a method as shown in FIG. 11 in which when a level of an input voltage is lower than that of an output voltage, a boosting switching regulator is operated, while when a level of the input voltage is higher than that of the output voltage, a step-down switching regulator is operated. A voltage detecting circuit 118 is operatively connected to a voltage power source 109 for supplying an input voltage in order to control a switch 119 on the basis of the input voltage. Then, when a level of the input voltage is lower than that of an output set voltage, the voltage power source 109 and a boosting side coil 103 are operatively connected to each other through the switch 119.
On the other hand, when a level of the input voltage is higher than that of the output set voltage, the voltage power source 109 and a boosting switch 105 are operatively connected to each other through the switch 119. That is to say, the switch 119 is operated with the voltage detecting circuit 118, whereby the switching of the boosting switching regulator and the step-down switching regulator is carried out to keep the level of the output voltage constant irrespective of the level of the input voltage.
Now, a conventional boosting switching regulator implements the controlling method as shown in FIG. 12 which is described as the prior art in JP 11-155281 A. First of all, a voltage level of Vout1 is detected, and then both of a voltage signal Va which has been obtained by dividing that voltage Vout1 through a division resistor 111 and a division resistor 112 and a reference voltage Vref which has been outputted from a reference voltage circuit 117 are amplified by an error amplifying circuit 113 to output an output voltage Verr. Next, a level of the output voltage Verr is compared with a triangular wave Vosc which has been outputted from an oscillation circuit 115 in a comparison circuit 114 to output a pulse which is used to control the boosting switch 107 shown in FIG. 11, thereby boosting an output voltage Vout so as to have to the voltage level higher than that of the input voltage. In addition, in the step-down switching regulator, similarly, the voltage level of Vout is detected, and then both of the voltage obtained through the resistive division and the reference voltage outputted from the reference voltage circuit are amplified by the error amplifying circuit. Then, the level of the outputted voltage is compared with the triangular wave outputted from the oscillation circuit in the comparison circuit to output a pulse used to control the step-down switch 105 shown in FIG. 11, thereby reducing the level of Vout down to a desired voltage level lower than that of the input voltage.
As described above, the operations of the switching regulator circuits are switched over to each other with the voltage detecting circuit, thereby carrying out the boosting and step-down operation.
However, since in the conventional boosting and step-down switching regulator, since the boosting switching regulator and the step-down switching regulator output the desired voltages, respectively, the voltage division resistors, the error amplifying circuits, and the coils are respectively required therefor. For example, there is encountered the problem in that while the input is switched over to another with the switch 119 when the operation is switched from the boosting operation to the step-down operation, the reduction in output voltage, a large-scale undershoot, a large-scale overshoot or the oscillation of the output voltage is caused until the switch has been perfectly switched so that the operation is perfectly switched from the boosting operation to the step-down operation. In addition thereto, there is the possibility that when the input fluctuation or the load fluctuation is carried out while the boosting operation and the step-down operation are switched over to each other with the switch 119, the output voltage may further oscillate.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide a boosting and step-down switching regulator controlling circuit in which resistors for voltage division, reference voltage circuits and error amplifying circuits which are respectively provided in a boosting switching regulator and a step-down switching regulator are made common to boosting switching regulator and the step-down switching regulator so that it is possible to reduce greatly the number of circuits.
In this case, a triangular oscillation circuit is controlled so as to oscillate a triangular wave for boosting and a triangular wave for step-down which are synchronous with each other but different in voltage level from each other, and a comparison circuit for boosting and a comparison circuit for step-down are respectively provided therein, whereby the control is carried out in such a way that if a level of an output voltage of one error amplifying circuit crosses the triangular wave for boosting, then a pulse used to control a switch for boosting is generated from an output terminal of the comparison circuit for boosting, while if the level of that output voltage of the one error amplifying circuit crosses the triangular wave for step-down, then a pulse used to control a switch for step-down is generated from an output terminal of the comparison circuit for step-down. As a result, whether the boosting operation or the step-down operation should be carried out can be automatically judged to carry out the switching therebetween in the inside of the switching regulator.
It is another object of the present invention to provide a boosting and step-down switching regulator controlling circuit which is capable of reducing the power consumption or enhancing the efficiency.
In this case, while two coils are conventionally required to be provided respectively, in the present invention, the boosting and step-down operation can be carried out with only one common coil, and also when a given input voltage is set to a desired output voltage, only the boosting operation is carried out if the boosting is required, while only the step-down operation is carried out if the step-down is required.
In order to solve the above-mentioned problems, according to the present invention, there is provided a boosting and step-down switching regulator circuit in which an output voltage of one common error amplifying circuit is compared with a triangular wave for boosting and a triangular wave for step-down which are synchronous with each other but are different in voltage level from each other in respective comparison circuits. As a result, the boosting operation and the step-down operation can be readily switched over to each other to reduce the power consumption and to enhance the efficiency.